I have seen cases but i am not a pundit on it. Well What i think is "two ppl from different castes get married and their progeny will be of the  lower caste (among them). If one of them is Brahmin, then they will be Chhetri (which is considered one step down than initial Brahmin caste)." The  whole point of caste system is to classify ppl on a ladder system (not talking about historically) so the supriority and inferiority does exist. I agree Chhteri is a caste itself but it isone step down to Brahmins. If Brahmins did something unethical, as a punishment they are moved down. There are no castes like G.C, K.C instead they are the surname of "Chhetri" caste. 

p.s~ not to confuse you guys, I am not advocating the superiority or inferiority of any caste but just sharing my thoughts and opinion. I personally do not care about the caste but it will be nice understand the underlying theories.